Opened 9 years ago

Closed 9 years ago

#282 closed defect (invalid)

Strange behaviour observed in the HM-5.0 with quantization matrix

Reported by: matteon Owned by:
Priority: minor Milestone:
Component: HM Version: HM-5.0
Keywords: Cc: fbossen, ksuehring, davidf, jct-vc@…

Description

When using the quantization matrix the initial quantization scale (denoted as uiQ) is modified to obtain the scaled quantization scale (denoted as uiQW) according the following formula:

uiQW = (uiQ<<4)/scaling_list[n].

where n denotes the coefficient position inside a given BxB TU. The shift by four bits (i.e. the multiplication by 16) is needed because the quantization matrix values are computed by multiplying their floating point values (picked by the HVS model that SONY is currently considering) by 16 and rounding them the nearest integer.

In this setting, the following issue has been observed when the quantization matrices are used (i.e. --ScalingList=1). Suppose to provide the encoder with quantization matrices whereby all the values are equal to 16, from the previous formula it yields that uiQW = uiQ. In this case, the encoder that runs with these (special) quantization matrices must produce the same reconstructed sequence (i.e equal pixel-by-pixel) that would be produced when no quantization matrix is used. This happens to not be the case for the current HM-5.0 release. Attached there are also the log files for the first 8 frames of race_horses sequence, QP = 32, ld_he. As may be noted the PSNR for both case is different. The rate is different too but this is expectable as the encoder that uses quantization matrices must transmit them and thus ends up with a higher bitrate.

Attachments (1)

logs_HM-5.0_qmatrix.zip (2.9 KB) - added by matteon 9 years ago.

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Change History (5)

comment:1 Changed 9 years ago by DefaultCC Plugin

  • Cc fbossen ksuehring davidf added

Changed 9 years ago by matteon

comment:2 Changed 9 years ago by ksuehring

--ScalingList=1 uses the stored default quantization matrices. --ScalingList=2 uses the values provided in the parameter file. I think this needs better documentation.

comment:3 Changed 9 years ago by matteon

  • Resolution set to invalid
  • Status changed from new to closed

Ok, I have done the test with --ScalingList=2 and now it works! Thanks!

comment:4 Changed 9 years ago by davidf

  • Cc jct-vc@… added
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